Showtime's Masters of Sex just wrapped up its first season on Sunday night, and I can safely declare that this thoughtful, provocative and intelligent show is one of the best of the year, if only slightly overpraised by some critics who proclaimed it the second coming of Mad Men.

That it is not (that's coming from an intensely devoted Mad Men fan), but it does have quite a bit to recommend itself so far. Starting with the two lead performances, sure to be nominated for Emmys next year (if they're not, it'd be criminal). Michael Sheen and Lizzy Caplan play William Masters and Virginia "Ginny" Johnson, the famed sex pioneers in the 1950's, who partnered together and published the book Human Sexual Response in 1966, which forever changed understanding about what happens to the human body during sex. The first season of this series took place over about a year (1956-57) and documented the beginning of their unusual relationship and collaboration. Masters and Johnson were unorthodox from the start, and quickly embarked on their own sexual relationship as participants in the study they were conducting, although Masters was married and the two would not marry themselves until 1971, when he finally left his wife.

Michael Sheen plays Dr. Bill Masters as an uptight stick in the mud, who's obsessed and in love with his work more than any one person. His attachment to Virginia develops instantly and at the same time ambiguously, as the series appropriately portrays their connection as being fused in part by the work, but a certain kind of love is surely growing as well between them. Despite an occasionally shaky America accent, Sheen conveys Masters' inner torment over his emotions and interactions with others in beautifully subtle shades, as well as his intense attraction to Virginia and egomaniacal drive to be recognized as having accomplished something as a scientist that will change the world. Some have found his character to be unbearably unlikable, in contrast to other TV antiheroes like Don Draper, Walter White and Tony Soprano, who were all in some ways, still charismatic and likable despite their detestable actions- but I think the uncompromising way that Masters is portrayed actually makes him more interesting, and a welcome difference in a TV world where everyone now wants their own charismatic antihero.

Lizzy Caplan's Virginia, by contrast, is the heart and soul of the show- a very modern woman in a 1950's universe. She's twice divorced, raising two little kids, and sexually free and uninhibited in a way very few women were at the time. In real life she also functioned as the opposite of Masters' antisocial personality, and her warm and friendly nature was what helped recruit volunteers into the study and helped the two of them later on to become celebrities and regular fixtures on talk shows. Caplan is terrific, and her inner and outer passions are expressed so fully that we feel very early on that we know her, and the development of Virginia and Bill's relationship is fascinating to watch and what for me, drives every moment of this show.

Of course, no series survives on just two characters, and that's where my nitpicking comes in. The supporting characters on the show, while played by some very good actors, have all proven to be far less interesting to me than anything directly involving Masters and Johnson. And that can be a problem when episodes have to vary between subplots involving people you're essentially uninterested in. The best of the supporting cast and storylines were undoubtedly those related to Lloyd Bridges and Allison Janney as the closeted provost of Masters' university and his sexually repressed wife. The two of them turned in fantastic performances as an unhappily married couple, and the show took the time to delve deep into Bridges' character's inner torment as well as Janney's. Janney especially should be another lock for an Emmy nod (and win) next year.

But the two most problematic characters on the show took up even more screen time to far less dramatic effect, and that's a problem that I hope will be ironed out by next season, because it's no slam at all on the actors. Caitlin Fitzgerald is Bill's wife Libby, and her main plotline throughout the season was her ongoing quest to get pregnant in spite of BIll's low sperm count. Fitzgerald is sweet and likable in the role, but her desperation to have a baby was never that interesting for me, not in the least because in real life, Bill and his wife did have two children and so this was not a great source of suspense overall. The other problematic character is Ethan, a young doctor at the hospital in love with Virginia, played by Nicholas D'Agosto. It may be that the writers put this character in a tough spot right off the bat by having him hit Virginia in the pilot (it's tough in current times for any one to come back from domestic violence), but Ethan's doomed relationship with his young fiance and ongoing attempts to win Virginia back just never won me over. His late season interactions with Ginny's ex-husband finally started to prove interesting, but it was too little too late, as the season finale had him heading off to California with me hoping he never comes back... but I suppose we'll hear what the writers have to say about that next season.

Masters of Sex wants to explore all kinds of sexual issues, including homosexuality and women's health (which in the 1950's was scarily primitive), and to challenge and face the gender divide between men and women when it comes to sexual science. But the explicit nature of the content is really no more graphic than most cable shows these days (if you're looking for that you'll see a lot more of it on something like Game of Thrones, for example). This is thought-provoking, intelligent, genuinely adult programming aimed at that audience, and I can't wait to see Masters and Johnson reaching new conclusions about sex and about themselves, for hopefully many seasons to come.